Machine for blow-molding containers, with means for orienting the preforms in the blow mold

ABSTRACT

A blow molding machine including at least a blow mold ( 12 ), wherein is introduced a preform ( 14 ) previously produced by injection molding, and a blow nozzle ( 22 ) for injecting pressurized air into the preform ( 14 ). It is equipped with a device for orienting the preform in the mold, the device including a grip member ( 30 ) adapted to grip the preform ( 14 ) by its neck ( 18 ) when it is engaged in the mold ( 12 ); a device ( 66 ) for driving in rotation the grip member ( 30 ); a device for detecting ( 70 ) at least a reference angular position of the preform ( 14 ); and a control device to cause the grip member to rotate until the detecting device detects the reference angular position of the preform.

The invention concerns the field of machines for manufacturingcontainers from thermoplastic material.

More particularly, the invention concerns blow-molding machines in whichcontainers are manufactured from plastic material, starting with aperform previously obtained, for example, by injection molding.

Such a machine has at least one blow-mold station with a blow mold inwhich a preform is engaged in such a way that its neck opens to theexterior of the mold. The blow-mold station has a blow pin that ismovable between a retracted position and a blow position in which it issealably held against the mold or against the neck of the preform inorder to introduce the blow fluid under pressure into the preform.

Machines of this type are currently used to manufacture polyethyleneterephtalate (PET) bottles and jars. In order to achieve good precisionin the shape of the bottle, especially in areas of complex shapes,relatively high blow pressures are used. Thus, when the blow fluid isair, the blowing is generally done under a pressure of around 40 bars.This high pressure allows the material of the preform, which has beenpreviously heated, to be forced against the walls that form theimpression of the mold. In most machines, a stretch rod is insertedaxially into the preform until it comes to rest against the closed endof the bottom of the preform at the same time as the pressurized fluidis injected. In this way the stretch rod makes it possible to bettercontrol the axial deformation of the preform during the blow-molding ofthe container.

In such a method of obtaining a container, the neck of the container isformed directly into its final shape during the injection molding of thepreform. This neck generally is threaded to allow the cap to be screwedon to the container.

In some cases, it will be necessary to maintain a particular angularorientation of the preform with respect to the blow mold. Such is thecase when neither the body of the container that one wishes to form, northe cap with which one wishes to close it, is a body of revolution. Inthis case, it is generally desired that the cap, once it has beencompletely screwed on to the neck of the container, have a very specificorientation with respect to the body, particularly for aestheticreasons. In this case, it is the angular arrangement of the threading ofthe neck with respect to the body of the container that will determinethe final position of the cap when it has been screwed on.

Also, it is necessary to provide means for angularly orienting thepreform with respect to the blow mold, since it is this mold that givesthe body of the container its final shape.

A purpose of the invention, therefore, is to propose means of orientingthe preform that are sufficiently precise to ensure a perfect angularorientation of the preform during the machine's entire manufacturingprocess.

To that end, the invention proposes a machine for blow-moldingthermoplastic containers, of the type having at least one blow-moldingstation having a blow mold in which there is a cavity in the final shapeof the container to be produced, of the type in which a preformpreviously produced by injection molding is engaged in the cavity insuch a way that only one open upper end of the preform, its neck,extends outside the mold, of the type in which the blow-molding stationhas a blow pin that is axially moved against the open end of the preformin order to inject pressurized air therein so as to mold the preforminto the final shape of the container,

characterized in that the blow-molding station has a device fororienting the preform in the mold, said device being composed of:

a preform gripping device that can grasp the preform by its neck when itis engaged in the cavity of the mold;

a drive device for driving the gripping device in rotation to turn thepreform around its axis;

a device for detecting at least one angular position of reference of thepreform; and

control means that are suitable for controlling the drive device inorder to cause the rotation of the gripping device until the detectiondevice detects the angular position of reference of the preform.

According to other characteristics of the invention:

the control means are suitable for causing a rotation of the grippingdevice and of the preform by a predetermined offset angle from theangular position of reference;

the gripping device is carried by the blow pin;

the device for detecting the angular position of reference of thepreform has an optical detector that can detect a reference mark made onthe neck of the preform;

the blow pin has a body that is axially movable between an upperretracted position and a lower working position, and the body can bemoved into an intermediate axial position of orientation in which thegripping device grasps the preform in order to be able to orient itangularly;

the blow pin body, when moving from its retracted position to anintermediate position, carries with it the gripping device which movesfrom a retracted position to a position of gripping and orienting thepreform, and when the blow pin body is moved from its intermediateposition to its working position, the gripping device remains stationaryand is moved relative to the blow pin body by elastic return means;

at its lower end, the blow pin has a bell which, when the blow pin bodyis in the working position, sealably presses against the upper surfaceof the mold, around the neck of the preform, and the bell is axiallyintegral with the blow pin body, but movable in rotation around the axisof the blow pin;

the bell and the gripping device are integral in rotation with eachother while being axially movable with respect to each other;

the bell has an external toothed wheel by which it is driven in rotationby the drive device;

the machine has several blow-molding stations that are mounted on arotary carrousel, and each blow-molding station has a preformorientation device.

Other characteristics and advantages of the invention will appear fromthe following detailed description as well as from the attached drawingsin which:

FIG. 1 is a general diagrammatical view in axial cross section of oneform of embodiment of a blow-molding station according to the invention;

FIGS. 2 to 4 are more detailed views of the blow pin and of theorientation device according to the invention, the blow pin beingrepresented respectively in its three axial positions of retracted up,intermediate orientation, and lower working position; and

FIG. 5 is an exploded view in perspective illustrating the couplingsystem between the gripping device and the blow pin bell.

Illustrated in FIG. 1 is a blow-molding station for a containerblow-molding machine. The example illustrated concerns a machine forblow-molding wide-neck containers, also called jars, but the inventioncan be adapted for other machines, and in particular to bottlemanufacturing machines.

The blow-molding station 10 has, in a known way, a blow mold 12 that isgenerally made in two or three parts that are movable with respect toeach other in order to allow a preform 14 to be introduced into the moldcavity 16, formed inside this mold 12, and to allow the container to beremoved from the mold after the blowing operation.

The preform 14 is in the form of a hollow body obtained by injectionmolding and it generally has an axial symmetry of revolution. Thepreform is thus closed at one axial end, which will arbitrarily becalled lower, and open at its upper end. This upper end, which isintended to form the neck 18 of the container, is cylindrical ofrevolution around an axis A1, and has, for example, external threading.When the preform 14 is engaged in the mold 12, only the neck 18 extendsoutside the mold 12.

In the illustrated example, the blow-molding station is configured sothat the neck 18 of the preform 14 extends above the upper face of themold 12. The blow-molding station has a blow pin 20 that is placedaxially above the mold 12, and which is intended to be moved axiallydownward against the neck of the preform 14 in order to injectpressurized air thereinto and to force the material of the preform bodyto be deformed and to take on the shape of the cavity 16 of the mold 12.

It should be noted that the terms “upper,” “lower,” “up,” “down,” etc.,used in the text refer to the configuration of the blow-molding stationas illustrated in the figures. However, the use of these terms shouldnot be considered as a limitation to the scope of the invention, whichwill also find application with other orientations of the blow-moldingstation.

According to one of the applicant's known designs of blow-moldingmachines, the blow pin 20 essentially has a tubular blow pin body 22that is axially movable in a fixed blow-pin holder 24 of theblow-molding station 10. A stretch rod 26, which is axially controlledby a cylinder or cam (not represented) to insert into the preform 14 andguide the axial deformation thereof during the blow molding, passesthrough the blow-pin holder 24 and the blow pin body 22 along the axisA1.

In the example illustrated, the blow-molding station is equipped with abell blow pin comparable to the one described in French patentFR-2,764,544. The blow pin body 22 is fitted at its lower end with abell-shaped part 28 that is open at its lower end to press sealably onthe upper face of the mold 12, around the neck of the preform 14 and notresting thereon. When the bell 28 is pressed against the mold, the blowpin is in sealed communication with the interior of the preform in orderto inject pressurized gas thereinto.

The blow pin body 22, and therefore the bell 28, can be axiallypositioned in at least three positions. In FIG. 2, the blow pin is inthe retracted up position in which it allows the preform to be loadedinto the mold 12, as well as the container to be removed after it isformed. In FIG. 4, the blow pin is illustrated in the working positionin which the bell 28 is pressed against the mold 12. The movements ofthe blow pin can be controlled in different ways, particularly throughthe use of a multistage pneumatic cylinder (not represented). Accordingto the invention, the blow-molding station has means for orienting thepreform 14 around the axis A1 after it has been inserted into the mold12.

As can be seen, the blow pin is equipped with a gripping device 30 thatgrasps the preform 14 when the blow pin body is moved axially from itsupper position to an intermediate position illustrated in FIG. 3. In theform of embodiment illustrated in the figures, the gripping device 30 isreceived inside the bell 28 and is designed to grasp the preform 14 bythe inside of the neck. However, as a variation, it could be designed tograsp the neck of the preform by the exterior, particularly in the caseof performs having a small-diameter neck.

As shown particularly in FIG. 5, the gripping device 30 has anappreciably tubular shaft 32 with axis A1 onto the lower end of which isscrewed an annular collar 34, the outside diameter of which correspondsto the inside diameter of the neck of the preform. At its periphery, thecollar 34 has an elastic snap ring 36 that holds the preform on thegripping device 30 when the collar 34 is axially engaged in the neck ofthe preform 14. At the moment of the engagement, the presence of anexternal radial flange 38 is of assistance. Said flange is at the baseof the neck 18 and allows the preform to rest on the upper face of themold 12. The collar 34 can thus engage in the neck 18, in spite of theeffort of engagement due to the presence of the snap ring 36. Thefigures show that the collar 34 has an upper rim 35 that can pressagainst the upper edge of the neck 18. However, the intermediateposition of the blow pin 20 will preferably be adjusted so that, forthis position, the rim 35 is not yet pressed against the neck 18 of thepreform 14.

According to one aspect of the invention, the gripping device 30 isintegral with the bell 28 in rotation around the axis A1, which can turnaround this axis with respect to the blow pin body 22 at the lower endof which it is attached. Also, the bell 28 is axially integral with theblow pin body 22 but the gripping device can slide axially with respectto this assembly when it is moved from its intermediate position to itslower working position.

To do this, as can be seen, the bell 28 is mounted on the blow pin body22 with a roller thrust bearing 40 and a ball bearing 22 [sic]interposed. The roller thrust bearing 42 can absorb the axial effortsthat occur when the blow pin body presses the bell 28 against the mold12. The ball bearing 42 provides precise guidance of the rotationbetween the bell 28 and the blow pin body 22. In this arrangement, thelower end of the blow pin body 22 is received inside the upper end ofthe bell 28.

However, to preserve a sufficient guide length, the shaft of thegripping device 30 extends into the lower end of the blow pin body 22.In order for the bell 28 and the gripping device 30 to move in rotation,a connecting part 44 is provided that is integral with the bell 28.

The connecting part 44 has a tubular section 46 that extends axiallyinto the blow pin body 22 and which is therefore radially interposedbetween said body and the shaft 32 of the gripping device 30. At thelower end of the tubular section 46, just beneath the lower end of theblow pin body 22, the connecting part 44 has an annular mounting flange48 that extends radially outward and is attached to the bell 28, forexample by means of screws 50. The connecting part 44 is thus completelyintegral with the bell 28, both in axial translational movement as wellas in rotation around the axis A1.

As illustrated in FIG. 5, the upper end of the tubular section 46 of theconnecting part 44 has two notches 52 in parallel axial edges. The twonotches open out into the upper end of the tubular section 46. In acomplementary way, the upper end of the shaft 32 of the gripping device30 has a cap 54, in this instance attached and welded, which has twoprotrusions 56 that are complementary to those of the notches 52. Whenthe shaft 32 enters the tubular section of the connecting part, theprotrusions 56 of the attached cap 54 are engaged in the notches 52 soas to allow a relative axial sliding of the gripping device with respectto the connecting part. However, the cooperation of the protrusions 56with the notches 52 prevents any relative rotation of these two parts.Thus, in addition to guiding the gripping device 30, the connecting part44 allows the gripping device 30 to slide axially with respect to thebell 28 while being integral in rotation with said bell.

As illustrated in the figures, the freedom of the gripping device 30 toslide is not total. Indeed, the gripping device is pushed downward bythe lower end of a compression spring 58 which extends axially into theblow pin body 22, and the upper end of which presses against thereaction surface of the blow pin body. Thus, the gripping device ispushed downward until the protrusions 54 of the cap 56 come to a stop atthe bottom of the notches 52 of the connecting part 44. This restingposition of the gripping device 30 is the one illustrated in FIGS. 2 and3. It will be noted that the effort exerted by the spring 58 on thegripping device 30 should be greater than the axial effort of engagementof the collar 34 in the neck 18 of the preform.

When the blow pin body 22 is moved to its lower working position inwhich the bell 28 is pressed sealably on the upper face of the mold, therim 35 of the collar 34 prevents the gripping device 30 from descendingany farther because it is resting on the preform, which in turn isresting on the mold. Also, the possibility of relative sliding of thegripping device and the bell is necessary to allow the blow pin to reachits lower position, the spring 58 then being compressed between thegripping device 30, which remains fixed, and the blow pin body 22 whichis descending, as illustrated in FIG. 4.

In this working position, it can be seen that the stretch rod 26 canmove axially through the gripping device in order to penetrate insidethe preform 14, while still leaving enough radial space between the rod26 and the inner wall of the shaft 32 so that the pressurized air can beinjected into the preform. It will also be noted that vent holes 60, 62are made in the shaft 32 and in the collar 34 of the gripping device 30in order to make it possible to preserve at all times an equal pressurein the blow pin 22, in the container in the process of formation, and inthe space delimited by the bell 28 above the mold, in order to preventthe neck 18 of the preform 14 from becoming subjected to a pressuredifferential that could deform it. Also, when the blow pin is in theworking position, the bell is pressed onto the mold 12 and therefore cannot turn around the axis A1, which also blocks any rotation of thegripping device 30. Said device then in turn blocks any rotation of thepreform 14, simply as a result of the adherence induced by the axialeffort applied by the spring 58, which is compressed.

However, when the blow pin is in its intermediate position illustratedin FIG. 3, it can be driven in rotation by a device 64 of the typeillustrated in FIG. 1. This device is essentially composed of anelectric motor 65 (as well as its control module) which controls therotation of a pinion gear 66 with axis A2 parallel to axis A1. The bell28 has an external toothed wheel 68 that meshes with the pinion gear 66,so that the motor 65 can turn the bell 28, and by turning the bell,turns the gripping device 30. The pinion gear preferably has an axiallength such that the pinion gear 66 and the wheel 68 always remainengaged, regardless of the axial position of the bell 28. Indeed,although the connection in rotation is really only essential when theblow pin is in the intermediate axial position of indexing, thisarrangement makes it possible to avoid any re-engagement problem.

As can be seen in the figures, the blow-molding station according to theinvention also has a device for detecting 70 an angular position ofreference of the preform. In the example selected, this is an opticaldevice that can detect a reference mark made on the neck 18 of thepreform 14. For example, the device could have a laser beam aimedtangentially at the neck of the preform, and it is then able to detect areference mark in relief 72 made on the preform.

It would also be possible to optically detect a notch made on the flange38 or a mark of colored ink. In the same way, an electro-mechanicaldetection device could be used.

The orientation of the preform as a result of the device according tothe invention can be done by carrying out the following steps. Thepreform 14 is first introduced into the cavity 16 of the mold and themold is then at least partially closed. The blow pin 22, initially inthe upper retracted position, is lowered to its intermediate position sothat the gripping device 30 can grasp the preform 14 by the neck 18.

The electric motor 64 causes the rotation of the bell 28, which drivesthe gripping device 30 by means of the connecting part 44. The lattercauses the preform 14 to pivot around its axis A1, the preform not beingclamped in the mold 12. When the optical device 70 detects that thereference mark 72 has reached a predetermined position, the system thenknows that the preform has reached an angular position of reference withrespect to the mold. If a device is used at a high speed of rotation andthe inertia of the motor causes the reference position to be passed upduring this first approach, the motor could also be controlled in theopposite direction to return to the exact position of reference.

From this position, the motor can be stopped and the preform held in theposition of reference, or the bell can be turned to a predeterminedoffset angle to place the preform in a new angular position that willstill be perfectly determined with respect to the position of reference.This possibility of an offset with respect to the position of referenceallows great freedom concerning the placement of the reference mark,which can therefore be easily created when the preform is injectionmolded, while taking into account the geometric constraints ofstripping.

Next, the blow pin 22 can be controlled downward to its working positionfor the blow-molding of the container, and when blow molding iscomplete, the blow pin 22 can be raised again directly to its retractedupper position so that the container can be removed from the mold.

With this type of blow-molding station, the orientation of the preformwith respect to the mold at the moment of the blow-molding can bedetermined with great precision, in a relatively short time, for exampleless than 500 ms. Consequently, this type of blow-molding station can beintegrated into a high-speed blow-molding machine having severalblow-molding stations distributed around a continuously driven rotarycarrousel, each station being fitted with its orientation device.

The invention just described is based on a preferred form of embodimentthat is illustrated in the figures. This form of embodiment, which usesan optical detector that controls an electric motor, makes it possibleto obtain results of good accuracy with respect to the orientation ofthe preform, and with good repeatability.

However, other variations of embodiment are possible. Thus, the drivedevice as described can be replaced by equivalent systems. In this way,the electric motor could be replaced by a pneumatic motor, or the devicecould be made in the form of a rack operated by an electric or pneumaticcylinder and meshing with the toothed wheel of the blow pin. Also, aperson skilled in the art could easily define variations of the preformgripping device, without going beyond the scope of the invention.

What is claimed is:
 1. Machine for blow-molding thermoplasticcontainers, of the type having at least one blow-molding station (10)having a blow mold (12) in which there is a cavity (16) in the finalshape of the container to be produced, of the type in which a preform(14) previously produced by injection molding is engaged in the cavity(16) in such a way that only one open upper end of the reform, its neck(18), extends outside the mold (12), of the type in which theblow-molding station (10) has a blow pin (20) that is axially movedagainst the open end (18) of the arm (14) in order to inject pressurizedair therein so as to mold the preform into the final shape of thecontainer, characterized in that the blow-molding station (10) has adevice for orienting the preform (14) in the mold (12), said devicebeing composed of: a gripping device (30) that can grasp the preform(14) by its neck (18) when it is engaged in the cavity (16) of the mold(12); a drive device (64) for riving the gripping device (30) inrotation to turn the preform (14) around its axis (A1); a device fordetecting (70) at least one angular position of reference of the preform(14); and control means that are suitable for controlling the drivedevice in order to cause the rotation of the gripping device (30) untilthe detection device detects the angular position of reference of thepreform (14).
 2. Blow molding machine according to claim 1,characterized in that the control means are suitable for causing arotation of the gripping device (30) and of the preform (14) by apredetermined offset angle from the angular position of reference. 3.Blow molding machine according to claim 1, characterized in that thegripping device (30) is carried by the blow pin (20).
 4. Blow moldingmachine according to claim 1, characterized in that the device fordetecting the angular position of reference of the preform (14) has anoptical detector that can detect a reference mark (72) made on the neck(18) of the preform (14).
 5. Blow molding machine according to claim 3,characterized in that the blow pin (20) has a body (22) that is axiallymovable between an upper retracted position and a lower workingposition, and in that the body (22) can be moved into an intermediateaxial position of orientation in which the gripping device (30) graspsthe preform (14) in order to be able to orient it angularly.
 6. Blowmolding machine a ding to claim 5, characterized in that the blow pinbody (22), when moving from its retracted position to an intermediateposition, carries with it the gripping device (30) which moves from aretracted position to a position of gripping and orienting the preform,and in that, when the blow pin body (22) is moved from its intermediateposition to its working position, the gripping device (30) remainsstationary and is moved relative to the blow pin body (22) by elasticreturn means (58).
 7. Blow molding machine according to claim 5,characterized in that at its lower end, the blow pin (20) has a belt(28) which, when the blow pin body (22) is in the working position,sealably presses against the upper surface of the mold (12), around theneck (18) of the preform (14), and in that the bell (25) is axiallyintegral with the blow pin body (22), but movable in rotation around theaxis (A1) or the blow pin (20).
 8. Blow molding machine according toclaim 7, characterized in that the bell (28) and the gripping device(30) are integral in rotation with each other while being axiallymovable with respect to each other.
 9. Blow molding machine according toclaim 8, characterized in that the bell (28) has an external toothedwheel (68) by which it is driven in rotation by the drive device (64).10. Blow molding machine according to claim 1, characterized in that ithas several blow-molding stations (10) are mounted on a rotarycarrousel, and each blow-molding station (10) has a preform orientationdevice.